To me, the SVT 4 Pro is simply one of the best gigging amp ever. Very well designed, offers so much bells and whistles for any bass player. The amp has two internal amplifiers. Capable of working together (mono) or independently (stereo). In stereo, the amp is capable of going down to 2 ohms per side. I've played venues where I could drive 2 Ampeg 810 behind me. That amp is a workhorse. Those who bash this amp never used it or misused it. Tonally, exactly the same as my Mesa Carbine M9: Super massive in the low department, super clean, super dynamic. But the SVT 4 has 3 tubes instead of one for the M9.
Compared to a SVT-CL, the CL produces natural harmonics SS or hybrid head don't let through. But to me the SVT 4 Pro sounds 90% alike. A bit darker, but way more headroom and heaviness. And half the weight of the CL.
One advice for pretty much any Ampeg amps: Don't use the master knob to find a good sound. But crack the GAIN!!! Personnaly I set the master at 75% and use the gain knob as volume knob. That's the secret to have a dynamic, warm and powerful SVT 4 pro.
One thing to care about: If you put it in a rack. The SVT4 needs room to breath. Don't forget a 1200W will produce a loooot of heat! A lack of room will trigger the thermal security to kick in, reducing the power to avoid any grave problem. This happened to me once, drilled holes in my rack, never ever happened since then.